1. Field of the Invention:
This invention relates to computer systems and, more particularly, to circuitry for converting coordinates stored in rectilinear coordinate systems into coordinates which may be conveniently used for scanning information to the output display of a computer system.
2. History of the Prior Art:
A major problem in utilizing computers to provide graphic displays is that for a single frame of graphical material to be presented on a cathode ray tube (CRT), it is necessary to store an indication of the information which is to be displayed for each position (pixel) of the cathode ray tube. With large and detailed displays, the number of pixels on the cathode ray tube may be approximately one thousand or greater in a horizontal direction and a like number in the vertical direction giving a total of approximately one million or more pixels about which information is to be stored. In a preferred system which is capable of providing a number of different colors on the cathode ray tube, each of these pixels contains eight bits of digital information specifying the particular color output. Consequently, approximately eight million bits of information needs to be stored for each frame to be presented at the output.
Not only does color information have to be provided for each pixel for each frame of the display, but in generating graphic displays, the usual method of determining the shapes of figures requires that various algorithms be applied to the geometric vertices of those figures. If this information is handled by the software of the system, computing the positions of each point to be displayed and determining the data to be displayed at that point shows the operation of the system to a point where operations such as animation are essentially impossible. For this reason, various systems utilizing hardware to speed the operation have been suggested. One method for speeding the operation is to use two output frame buffers, and load one while the other is being scanned to the display. Such a system significantly speeds the operation but requires essentially twice as much storage.
A new output display system has now been devised which utilizes a unique philosophy of graphic figure storage whereby high speed graphics may be realized using only a single output display buffer. The system, essentially, is based on a definition of a graphical figure (shape) which considers the shape to be composed of a number of subportions which are quadrilaterals. Circuitry is then provided for rapidly building quadrilateral images by handling only information regarding four vertices.
In providing such a hardware system to rapidly process information for a computer output display, it has been found convenient and substantially less time consuming to deal with the information regarding the address of the data to be presented on the display in rectilinear coordinates. On the other hand, the same data must be serially scanned to the cathode ray tube output display for convenient use. Most systems for translating such information themselves provide inordinate delays to the presentation of the graphics information. In order to eliminate these delays, hardware implementations of the software transfer algorithms have been utilized, but these require such large amounts of digital hardware that they have been economically unfeasible. Moreover, such systems have been able to handle either a single level of detail (resolution) on the display or some power of two representation of that level of detail.
It is, therefore, an object of the present invention to speed the operation of computer systems.
It is another object of the present invention to provide circuitry for handling in hardware the manipulations of graphical material which have in the usual case been handled by software of the computer system.
It is another object of this invention to provide a computer graphic display system capable of handling a number of different levels of detail (resolution) on a computer output display which levels are not simply variations of powers of two.
It is an additional object of the present invention to provide circuitry for scanning graphic information into a display register rapidly enough that a single buffer may be utilized for the display of animated programs.
A more particular object of the present invention is to provide circuitry for transforming coordinates represented in rectilinear form by X and Y values into values which may be scanned serially into a display buffer for ultimate display by a cathode ray tube or other output device.